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A SUMMARY EXPOSITION OF SAINT THOMAS 
AQUINAS'S PHILOSOPHY OF KNOWLEDGE. 1 

THE aim of the present article is to state briefly, not to dis- 
cuss, a theory. It does not purpose to justify, but simply 
to interpret it in a reliable and trustworthy manner, in strict con- 
formity with the tenets of the venerable system which for several 
centuries was the prevailing philosophical doctrine of the Western 
World. 

Thinkers of to-day begin to realize that there is more to be 
found in the works of the great authors of the scholastic period 
than was formerly supposed, and accordingly there may perhaps 
be aroused in some reflective minds a desire to look into the 
depths of the thought of a period, in which it has been too com- 
monly supposed that nothing was stored up but rubbish and use- 
less subtleties. The difficulty, however, is to get at the right 
meaning of those early scholastic philosophers, so as to under- 
stand their doctrines as they themselves understood them. 
Separated as they are from our times by a distance of several 
centuries, they are enclosed, so to speak, within the walls and 
barriers of a special dialect framed, used, and available for scho- 
lastic purposes only. The conciseness, as well as, at times, the 
prolixity of their style, altogether devoid of pretension to any 
literary merit, and the summary, rather algebraical character of 
their formulas, that aimed at nothing but expressing an idea with 
the greatest possible precision, often make interpretation a task 
of great uncertainty for the uninitiated. 

To such persons, therefore, as may care for a faithful and re- 
liable exposition, one that does not substitute the private views 
of the exponent for the genuine conceptions of the author, we 
offer the present essay as a contribution intended to convey to 
their minds the authentic doctrine of Aquinas, a doctrine which, 
on this particular subject, was that of his contemporaries gener- 

1 The author desires to express his thanks to Dr. Clarke Murray, of McGill Univer- 
sity, for helpful suggestions made by him in regard to the following article. 

6ll 



612 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

ally, concerning what may be considered, and has in fact become, 
since the days of Kant, the most controverted and most impor- 
tant of speculative problems — that of the philosophy of knowl- 
edge. 1 But since St. Thomas's views on human knowledge are 
essentially connected with his psychological system, it will first 
of all be necessary to give a short summary of the latter. 2 



If we should attempt to give a definition of the human soul, as 
St. Thomas himself would have formulated it, we should define it : 
" The substantial form of a physical organic body endowed 
with rational life." Anyone who is at all acquainted with 
the Ilepi To^z of Aristotle will, at the first glance, have dis- 
covered in the first member of the foregoing definition the equiv- 
alent of that which the celebrated Peripatetic gave of the soul 
considered in its generic aspect as the vital principle common to 
every living being, or as "the first entelechy (fundamental constitu- 
tive perfection) of a physical organic body;" 3 that is to say, that 
first fundamental constitutive perfection that raises the body in 
which it resides to the dignity of a real living organic body, by 
generating in it the vital impulse, the vital activity. What Aris- 
totle called ' first entelechy ' the scholastics used to render by the 
synonymous expression ' substantial form,' an expression which 
we cannot avoid and which we shall therefore explain some- 
what more fully. 

1 The author, being a member of the religious order to which St. Thomas him- 
self belonged, and having been for twelve years a student or teacher of his system, 
may venture to hope that he merits some confidence as an interpreter of the views of 
one whom he may style his brother and master. 

2 The doctrine of St. Thomas concerning the human soul may best be looked for 
in his Summa theologica, Part I, from question lxxv to question xc inclusive, where 
he treats the subject ex professo and in full, although in his characteristic scholastic 
manner ; also in the Contra gentes, Book II, from chapter lvi to chapter xc inclusive, 
again in the Qutzstiones disputata at the question De anima (twenty-one articles), 
and in his commentaries on Aristotle's three books De anima. St. Thomas deals 
with the subject of the human soul in other passages, but we content ourselves with 
mentioning those in which the exposition is most complete and systematic ; the same 
remark may apply also to the quotations that we are going to make further on, this 
article purporting to be a faithful interpretation, not a concordance. 

* 'TZvTe\6x ela $ TipiffTj auftaroc (jmainov bpyavixov {Jlspi ^tv^vr, Book II, c. I, 
line 44, Didot edition). 



No. 6.] AQUINAS'S PHILOSOPHY OF KNOWLEDGE. 613 

Spectroscopic analysis shows us that matter is everywhere 
identical throughout the sidereal world, while chemical analysis 
reveals to us the fact that all things are made of the same ele- 
mentary principles, the so-called simple bodies. If we omit 
for the present the question as to whether the given number of 
simple bodies that we admit nowadays cannot or will not even- 
tually be reduced to some smaller number, there is one thing, at 
all events, that we may safely assert, viz., that those simple 
bodies, whatever their real number may be, are all but various, 
primitive forms of one and the same nature, matter. For even 
granting that they are chemically quite unanalyzable through 
any material agency, there are still some features that all have in 
common, those that are characteristic of materiality. All, in- 
deed, have more or less extension ; all have weight, density, and 
the other properties that are inseparable from matter, wherever 
and under whatever form it can be found. We are therefore led 
by the simple observation of facts to conceive of some generic 
element common to all, attainable indeed by reason only, but 
which reveals itself to us under the primary forms of the simple 
bodies of which it is the common and radical substratum, the 
simple bodies being merely its primitive and original forms. 
This substratum was the primary matter, materia prima, of the 
Scholastics. 1 

Furthermore, experience reveals to us that, whenever, either in 
the organic or inorganic realm, some new combination takes 
place, the elements thus combined, either compound or simple 
bodies, seem to disappear — to melt mysteriously together into 
some new entity into which they are absorbed, the total sum of 
which has indeed the same weight, but, seemingly at least, prop- 
erties of a quite different nature from those of the component 
elements. The qualities of water, for instance, are admittedly 
altogether different from those of its elements, the gases hydro- 
gen and oxygen. Water, therefore, may be considered as being 
only virtually contained in both before combination. On the 
basis of this experimental fact, that matter, as it is found under 

l Cf. Zigliara, Summa pkilos., Cosmologia, Liber II, cap. ii, art. 2 et 3 ; Aquinas, 
Sum. theol., Part I, q. lxvi, 2. 



614 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

any form whatsoever, either in simple or compound bodies, may 
always be transformed chemically so as to be brought under 
some other, which is seemingly, at least, essentially different from 
the preceding one, the Scholastics laid down as a general prin- 
ciple that any natural being, either organic or inorganic, ought 
reasonably and upon good experimental grounds to be considered 
as made of two constitutive substantial elements, the original 
matter and its own proper form. The first was ever identical 
under all possible forms ; but the forms were always different 
from one another, either specifically, as the form of a dog is from 
the form of a tree, or numerically, as those of different trees of 
the same species. 1 

Let us also remark here in passing that the Scholastics distin- 
guished between the substantial form, which was a constitutive 
essential part, and the accidental form ; the latter being only an 
accessory and complementary determination supervening in the 
individual upon his constituted nature. Fluidity, for instance, or, 
in the case of frozen water, solidity, were only accidental forms of 
the water that was in itself substantially constituted by matter 
and the ' watery form.' The human soul also was a substantial 
form, the first act or entelechy of that physical organism, the 
human body. 2 It was the soul that generated in it the en- 
semble of activities, regularly and harmoniously cooperating, 
which we call life ; without the indwelling and immanent agency 
of the soul, that body would have remained inanimate, lifeless ; 
through it, it became a real ' physical organic body ' because a 
living one. 3 The soul, therefore, was residing in the body, not, 
as Descartes would have said, somewhat like a horseman sitting 

1 Cf. Sum. theol., Part I, q. 66, a. I and 2, and passim. The concept of matter 
and form, as every one knows, was no creation of the Scholastics ; they had simply 
borrowed it from the Greeks. For St. Thomas's interpretation of the Aristotelian doc- 
trine on that point, one may consult his Commentaries on Aristotle's Physics (De 
physico auditu), Book I, and on his Metaphysics, Book VIII. 

2 Cf. Sum. theol., Part I, q. lxxvi, a. I ; Contra gentes, Book II, c. 68. We 
should like to remind the reader that the following exposition of St. Thomas's psy- 
chology is a mere statement of his views. It would be impossible within such a 
narrow compass as that of the present article to attempt anything like a sufficient 
justification of them. 

3 Sum. theol., Part I, q. 75 > a - '• 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 615 

on his steed, or like a pilot in the ship that he guides, but as a 
constitutive principle forming by its combination with the body 
a single new being, to wit, the individual man, that was different 
from both, as water is from hydrogen or oxygen ; for the man is 
neither the soul nor the body but a compound of the two. 1 

This doctrine must appear very materialistic, and hardly recon- 
cilable with the spiritualistic creed which is the necessary ' pre- 
suppositum ' of Christian belief, if the human soul is to be con- 
sidered as entering into combination with a purely material nature 
like the body, and if it is to be regarded as exerting upon it that 
sort of quasi-chemical, or, one might say, fermentative action that 
generates in it the vital activity, just as the soul of a brute or 
the vital principle of a plant. 2 

Still that substantial form of a material body was considered 
by St. Thomas, at the same time, as immaterial and therefore 
simple. It was immaterial, because being able, as all will admit, 
to form some conceptions of immaterial objects, such as the 
Good, Virtue, God, etc., such conceptions could be the product 
only of proportionate and similar, that is to say, immaterial, oper- 
ations ; for even if necessarily accompanied, as has been abun- 
dantly proven by physiology, with material concomitants in the 
brain, those operations could not have reached an immaterial 
object if they had been essentially and exclusively material them- 
selves. Again, the idea of an immaterial operation cannot be 
understood without the idea of an immaterial faculty that produces 
it, and which in its turn points necessarily to an immaterial nature, 
from which alone it can spring. 3 

Being immaterial, the human soul is consequently immortal, 

1 Sum. thiol., Part I, q. 76, a. 8. This doctrine concerning the substantial union 
of the soul and the human body is now a dogma of faith in the Catholic Church since 
the definition that was formulated by the council of Vienne (France) in 1311. (Cf. 
Enchiridion symbolorum of Denzinger, No. 409, 9th edition, 1901, Wiirzburg. ) 
It is on this basis of the mutual, natural, and necessary correlation of body and 
soul that some eminent commentators of the master inferred that the human soul after 
death, being on account of its separation from the body in an unnatural or violent 
condition, required a future resurrection of that body, as some sort of natural right. 
The Church, however, has not adopted that inference. 

2 Cf. Ibid., Part I, q. lxxvi, a. I, 3, 4. 

s Cf. Ibid., Part I, q. 25, a. 2. 



616 THE PHILOSOPHICAL REVIEW. [Vol. XII- 

not by privilege, but by its nature, so that it cannot be other- 
wise conceived, 1 and therefore it cannot come into existence, ex- 
cept by creation, nor possibly be destroyed, except by annihila- 
tion, just like the primary quantitative elements of the simple 
bodies themselves. 2 

How, then, does Aquinas reconcile the seeming contradiction 
that exists between the concept of a spiritual soul and that of the 
same as ' substantial form ' of an organic body ? The solution 
of the apparent antinomy is to be found in the grand view in 
which, following Dionysius Areopagita, his mind embraced 
the whole world. 3 The divine wisdom that made the universe 
disposed the scale of beings in such an order of rising and 
gradual perfection, that every superior form virtually contains 
in its own perfection all the attributes that can be found in 
the inferior beings, together with its own superior characteristic 
properties, so that it may be laid down as a general principle in na- 
ture, that " Summum infimi attingit infimum supremi," the superior 
grades of perfection of any given being are to be found again as 
inferior perfections in some higher species, so that there is no gap 
in nature, which rather rises steadily through multiple intermedia, 
from the lowest to the highest organisms. 4 In plants, we find 
minerality, but associated and subordinated to the functions that 
are characteristic of the living beings, nutrition, growth, and gen- 
eration, under the vegetable form ; in the animal kingdom, we 
discover vegetative life, but associated with it that higher degree 
of activity which is peculiar to sensitive beings and manifests 
itself principally in locomotive power ; in man, we find at the 
same time minerality combined with vegetative and sensitive life, 
but subservient to moral and intellectual activity. That is why 
the ancients used to call man a microcosmns, for he was like a 
resume of the various perfections scattered through the universe. 
But since the human being possesses one superior order of facul- 
ties, those that fit him for a distinctly spiritual activity, it must 

1 Cf. Sum. theol., q. 95, a. 6, and Contra gentes, Book. II, ch. 79. 
2 Cf. Ibid., Part I, q. 90, a. 2. 

* Contra gentiles, Book II, ch. 68. 

* Let us remark in passing how nearly related to the evolutionary theory is the 
view that we mention here. 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 6lJ 

be admitted also that that organic body of which the soul is the 
substantial act or form, was raised by it to the participation of its 
own immaterial being, of its own intellectual and moral pursuits. 
It shared in them, as the subject required to support the exercise 
of those intellectual and moral operations, and as the instrument 
through which the soul comes in contact with the external material 
world. As man partakes of all the attributes of material beings, 
which are, so to speak, epitomized in him, while at the same time 
he partakes of the higher functions of intellectual and moral life 
along with the angels, he appears to us like a horizon ' in which 
heaven and earth unite, as the intermediary being through which 
material life blossoms, as it were, into spiritual and immaterial 
activity. 

Such, in brief, then, is the meaning of our definition of the 
human soul as " the substantial form (first act or entelechy) of 
a physical organic body endowed with rational life." 

II. 

A theory of knowledge based on such psychological founda- 
tions must logically follow the same plan in its systematic elabora- 
tion, as will become apparent from the remainder of this article. 
Like the soul from which it emanates, the cognitive power in man 
will be at the same time material and immaterial, or, to express it 
more accurately, will, although essentially immaterial, exercise 
some of its operations with the necessary concurrence of the body ; 
there will be in it something material and something immaterial. 
The faculties of the soul spring forth from its essence as the 
boughs from the stem of a tree, distinct from it but as a natural 
and necessary production of it. 2 The human intellect, therefore, 
is an efflux of the soul ; it is the eye through which it explores 
the material and even peers into the spiritual world, being, as the 
Scholastics would have said, ' a spiritual accident of a spiritual 
substance.' Nevertheless, all knowledge must develop from the 
data of sensuous perception, 3 and it is only through inferences 
and indirectly that it can rise to any immaterial notion concern- 

'Cf. Contra gentes, Part II, 68. 

2 Cf. Sum. theol., Part I, q. 77, a. I, 6. 

»Cf. Ibid., Parti, q. 84, a. 6. 



618 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

ing the immaterial world. A careful analysis of the process of 
intellection will help us to realize that fact, which the Scholastics 
expressed in the trite axiom, non est intellectus sine phantasmate 
— there can be no intellection without some picture in the 
imagination — not only as the starting point, but also as the nec- 
essary and indispensable subject of any operations of the intellect, 
even the most abstract and seemingly immaterial one. 1 Such 
a conception obviously must imply that there are for St. Thomas 
no innate ideas, since all knowledge must begin from sensuous 
perception. And, indeed, if by innate ideas we understand such 
concepts as we might have inherited ready-made, there are not 
for him, in the proper sense of the term, any innate ideas. 2 This 
is for him a simple statement of fact : it does not require any 
demonstration. Did not Aristotle, the philosopher — he whom 
we might term the prophet of the Scholastics — tell us that the 
individual human mind at the outset is like a tabula rasa on 
which nothing has as yet been written? 3 Such is undoubtedly the 
condition of the mental faculty of a child before the awakening 
of his intellectual activity. As a fact, therefore, man is not born 
with ready-made ideas, and in that sense there are not any ' in- 
nate ideas ' so-called. 

But if no ideas are innate in the human mind, there is never- 
theless in it an inborn tendency to frame some very definite ones 
which universally appear in it as soon as the first awakening of 
the intellectual faculty takes place ; for that awakening itself im- 
plies and involves the acknowledgment of the first principles 4 
which form themselves spontaneously in the intellect as soon as 
it comes in contact with ' intelligible ' objects ; exactly as the first 
contact of food causes the gastric juice to spring from the walls 
of the stomach. 

The simile is a very material one, but it may be pardonable to 
employ it in default of a better one ; and it may help us to realize 
the meaning of the Scholastics. The difference, however, is that 

1 Cf. Sum. theol., Part I, q. 84, a. 7. 
2 Cf. Ibid., q. 84, a. 3. 

a &o"rrep ev ypa/i/jaTsia a firfilv vwapxsi hrelsx 8 ' 10 - yeypa.fi/ii6vov (Tlepi 'ivxK, Bk. 
Ill, c. 4, no. II, Didot edition). 

* Sum. theol., secunda secundtz, q. xlvii, a. 6. 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 619 

the gastric juice is produced by the stomach alone, being secreted 
by its walls at the presence of a digestible object, but the latter 
contributes nothing to the substantial constitution of the said gas- 
tric juice : whereas the first principles are generated in the intellect 
by the intelligible object itself, and in fact they are nothing but 
mental conceptions based on, and representing, its most abstract 
and general feature, to wit : being, ratio essendi. 

When a photographic plate of slow action is exposed to light 
in a camera, if developed after a very short exposure, it reveals 
nothing but a vague and indistinct outline of the object, of which 
it was intended to reproduce the likeness. It is only after a suf- 
ficient exposure that the image of the object will have imprinted 
itself with all its details in perfect clearness of reproduction. So 
with the human intellect, the earliest idea that it receives at first 
sight from any object whatever is that very vague and indis- 
tinct notion that ' there is ' something before itself, that a being 
appeals to its cognitive power ; but it is only after a careful ex- 
amination and a progressive investigation, that it may hope to 
acquire a full knowledge of the said being in all its details. 

The idea of Being is therefore the very first intellectual im- 
pression that the human mind gathers, although confusedly, 
from the outward object. 1 That idea of Being, expressed in a 
negative formula, is the very first of all first principles, the prin- 
ciple of contradiction, viz., ' Being is not not-being.' All other 
so-called first principles of theoretical knowledge are nothing but 
various applications of that one and unique first principle. The 
principle of causality, for instance : ' Nothing takes place with- 
out there being some sufficient cause to account for the change,' 
simply means that no new being can come into existence, spring- 
ing from Naught, since the contrary would imply that Being and 
Naught are practically identical. A similar explanation might 
be given of all other first principles, bringing them all down to 
the principle of contradiction, if we could afford such a digression 
for the present. 

Those first principles, therefore, are the only ideas that might 
perhaps in a derived and secondary sense be called ' innate ideas,' 

1 Cf. Sum. theol., I a 2 ie , q. 94, a. 2. 



620 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

inasmuch as they form themselves naturally and uniformly in 
every human mind ; still, since they are generated from the 
potentiality of the intellect by the object, they come from with- 
out, and are of objective origin, although subjective as to their 
formation. 1 

All other ideas, those representing things or facts, are acquired 
by some mysterious intuition by which the human intellect reads 
into the nature of some given material object, and that process 
we are now going to try to investigate by means of psychological 
analysis. 2 

The process of intellection is naturally divided into two succes- 
sive stages, one which we have in common with the animals, the 
preliminary stage, the stage of sensuous and imaginative precep- 
tion ; the other, which is peculiar to man, is the stage of abstrac- 
tion, of properly universal or intellectual knowledge. Sense per- 
ception, considered in its general conditions, is easy to describe and 
presents no special difficulties. Any sensible object that appears 
before our senses is a complex of various qualities, visible, aud- 
ible, odorous, tactile, or gustatory. The sensorial apparatus of 
man will by its five organs, sight, hearing, smell, touch, and 
taste, separate each group of qualities from the others ; each one 
of them will find its own entrance, organized and adapted for it, 
into the sentient subject. All those qualities that first enter in 
separate groups will, in the next instant, be reunited into a sen- 
sible imaginative picture that will be the exact representation of 
that very individual object that stands before us, let us say a dog, 
for instance, or a tree. 

In the animals, knowledge stops at that stage ; there is no 
further progress ; the animal can imagine, remember, even form 
some instinctive judgments, but it cannot have universal ideas — 
it cannot think. In man there is something more : that raw ma- 
terial, that sensible and single picture of that individual dog, that 
individual tree may, by the mysterious process of intuition that 
we call abstraction, be converted, manufactured, into the intel- 
lectual universal representation of the tree in itself, or the dog 

•Cf. Zigliara, Summa philos., Log., No. 55. 
2 Cf. Sum. theol. , Part I, q. 85. 



No. 6.] AQUINAS'S PHILOSOPHY OF KNOWLEDGE. 621 

in itself, into the ' intelligible ' idea of the dog, the tree. In 
what manner, then, does that abstraction take place ? Every 
picture that is in the imagination appeals to the intellect, but the 
intellect may or may not, according to its present condition or 
circumstances, advert to it ; however, there stands the ' phan- 
tasm ' l before the intellectual faculty, apt to arouse its activity, 
ready for use. It is also admitted by all that a single individual 
phantasm is not sufficient to cause the intellect to act : it is only 
by the recurrence of similar appearances, that it is aroused into 
activity, and then spontaneously abstracts the universal from the 
singular. 

Let us now suppose that several individuals or instances have 
already appeared in the imagination, that they have left an en- 
during impress upon it, without however having succeeded, up to 
the present, in bringing the intellect to the act of manufacturing 
a universal idea. The intellect has remained inactive, it is in the 
condition of a looking-glass before which stands an object, but 
in which no reflection appears, because the object is, as yet, in 
the dark. 

But now the succession of similar experiences is sufficiently 
complete. A new 'phantasm,' clothed with all its sensible quali- 
ties, is offered again to the intellect, together with the remem- 
brances of past similar experiences ; then, as if by the turning of 
some electrical switch, a flood of intellectual light, if we may use 
the metaphor, flashes upon it ; the complex of sensible qualities, 
that is, the phantasm, assumes an 'intelligible,' immaterial condi- 
tion, and that immaterial mirror, the intellect, receives in itself 
the immaterial picture thus revealed, the universal abstract idea. 2 

Following the data of Aristotle, the scholastics therefore di- 
vided the intellectual faculty, in itself one and indivisible, into 
two powers — the active intellect, intellectus agens? and the pas- 
sive intellect, intellectus possibilis.* The first, the intellectus agens, 
is that power, that aptitude, inherent in the human mind, to dis- 

1 By the word ' phantasm ' the Scholastic philosophers understood the representa- 
tion of a thing as it is in the imagination. 
2 Cf. Sum. theol., Part I, q. 79, a. 2. 
9 Ibid., a. 3. 
4 Ibid., a. 10. 



622 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

cover and bring into prominence the universal, to illuminate the 
phantasm with intellectual light, we might say, so as to imma- 
terialize it. The intellectus possibilis, on the other hand, is the 
faculty of perceiving and assimilating the universal idea that has 
been evolved from the individual by the activity of the intellectus 
agens. It is the mirror in which the immaterial likeness of the 
object, the universal idea, reflects itself, when it has once been 
brought forward by the illuminating power of the intellectus agens. 
It is called passive, possibilis, from its aptitude to take up any idea ; 
but it is essentially active, as soon as it has acquired the idea. 
This it is that thinks, judges, reasons, organizes science, and so 
on ; it is the thinking mind itself, of which the intellectus agens 
is only the servant and the tributary. 1 There are, indeed, besides 
the first one that we have just described and that was called by 
the Scholastics simple apprehension, two other operations which 
are proper to the intellectus possibilis alone, viz., judgment and 
reasoning. When once in possession of several ideas through 
abstraction, the human mind may also mentally associate or dis- 
sociate them by judgments that are expressed in propositions ; 
again, it can evolve by reasoning some new judgment from others 
in which it is implicitly contained. These are the three funda- 
mental operations of the human intellect: perceiving, judging, 
reasoning; all others are more or less forms or complexes of 
these three. 

III. 

After having perused the preceding exposition of St. Thomas's 
doctrine on the human soul and the human intellect, one more 
question will naturally occur to a modern mind familiar with 
post-Kantian philosophy. What were the views of Aquinas con- 
cerning the value of human knowledge ? What was his stand- 
point in regard to the epistemological problem ? 

The answer to this inquiry allows of two different researches, 
viz., first, stating and defining that standpoint, and secondly, 
solving from a Thomistic point of view the difficulties that might 
be urged against it from a Kantian point of view. But as the 
second part of such a study would imply a critical examination 
1 Cf. Ojmsc. de potent, anima, ch. vi. 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 623 

of the Kantian system as a whole, we shall for the present refrain 
from such an attempt, and content ourselves with stating St. 
Thomas's position and defining his doctrines concerning the re- 
liability of our knowledge and the grounds on which it rests. 

As regards his general conclusions, he decided the question 
by vindicating the absolute objective value of human knowledge, 
although not, of course, the infallibility of the individual mind. 
When the intelligible universal idea has been evolved through 
the agency of the intellectus agens from the sensible phantasm, 
the question will arise, Where does that intelligible idea come 
from ? It cannot have come out of Naught, for this would be 
an utter impossibility ; the intelligence of man cannot, any more 
than any other finite being, create anything, not even an idea. 1 

It might be supposed that the idea is produced by the intellect 
itself from its own substance when it comes in contact with the 
object, just as a spark will spring from the pole of an electric ap- 
paratus when touched by the finger of the operator. Neither 
St. Thomas nor any of his contemporaries seem even to have 
considered such a hypothesis, to which, however, Kant's doc- 
trine of the a priori forms would come very near. St. 
Thomas would very likely have answered that, according to all 
appearances, whereas the electric spark, whatever may be the 
nature of the object that comes in contact with the pole of the elec- 
tric machine, is always the same, different sorts of objects give 
rise in the mind to different ideas of objects with perfect and in- 
fallible mutual correspondence, so that the variety of ideas cannot 
be satisfactorily accounted for, except by the diversity of the ob- 
jects that generate them in the human mind. 

If it be further urged, and this is more distinctively the Kantian 
position, that there are positive and de facto motives to distrust 
the testimony of our intellectual faculty concerning the external 
realities, the answer, as already stated, would involve a critical 
examination of the various motives brought forward to batter 
down the authority of reason ; we are consequently obliged to 
decline to attempt that in the present article. One thing, how- 
ever, we shall not hesitate to state in advance, viz., that neither 

'Cf. Sum. theol., Part I, q. 45, a. 5. 



624 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

the a priori forms of the sensibility, nor the a priori categories of 
the understanding, nor the antinomies of reason would have dis- 
turbed the serene confidence of St. Thomas in the objective 
value of our knowledge ; for all those objections he would have 
discarded, maintaining that they did not apply to his view of 
Space and Time, to his Categories, to his arguments concerning 
God, the World, and the human soul. 

For Aquinas, therefore, if mind discovers the idea in the 
phantasm of the sensible individual, it is because the idea is con- 
tained in that sensible individual as a letter in its envelope or a 
diamond within its gangue ; indeed, it is nothing but the sub- 
stantial form of the thing in itself ideally reproduced in the intel- 
lectus possibilis, as the likeness of a person in a looking-glass or 
on some photographic plate. 1 

Now if the substantial form is capable of being so ideally 
reproduced, it is because it is itself an idea, a concept of the 
divine mind embodied in matter, the archetype of which exists 
in God, and which has been enclosed in it by Him. 2 Hence it 
follows that the cognitive process is nothing other than a com- 
munion with the divine mind through the intermediary of things, 3 
a deciphering of the book that He has written in Nature for our 
instruction ; for the whole universe is the handiwork of God and 
the heavens declare His glory (Ps. 19). Another objection may 
be raised, viz., since the idea is universal whereas the individual 
is singular, how can the one be a faithful picture of the other ? 
In that form, apparently the only one in which the epistemological 
problem appealed to the minds of mediseval philosophers, it gave 
rise to the celebrated quarrel about the Universale. 

Without reciting here the various opinions that were set forth 
at the time, we shall simply reproduce Aquinas's solution of that 
question. But there is first of all a preliminary observation that 
will force itself upon our attention : those features, those modes, 
universality or singularity, are in themselves accidental or external 
to the essential constituents of the ' form ' in itself. 4 

!Cf. Sum. theol., Part I, q. 85, a. 2. 

2 Ibid., q. 14, a. 8. 

3 Ibid., ad 3 um . 

* Ibid., q. 85, a. I, ad l um ; Opusc. de ente et essentia, ch. 4. 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 625 

Just as, in the case of a photographic picture, the likeness of a 
man must not be supposed to be unlike to him in reprcesentando 
because it is apt to be reproduced in an indefinite number of 
paper prints, so an ' intelligible ' likeness, though it be universal, 
remains the same in the essential features, and universality is a 
merely extrinsic condition that makes no difference to its repre- 
sentative value. 1 

But, moreover, universality is not a creation of the intellect ; 
it is derived from the objective world, it has its objective counter- 
part. It is because the mind has discovered the same feature in 
several individuals that it is naturally induced, from the very 
objective condition of things, to conceive that feature as one ele- 
ment, possessed in common by several singulars, as a universal. 
Universality, therefore, as it is in the mind, has for its objective 
foundation that plurality by means of which it is participated in 
by several individuals in the external world. 

It is not an arbitrary or spontaneous creation of the mind ; it 
represents something, to wit: the fact that one and the same 
reality or portion of reality is to be or can be found in several 
distinct individuals, and we may therefore conclude that ' nothing ' 
is to be discovered in the idea which is not somehow in the 
object, according to the trite scholastic axiom : Nihil est in in- 
tellectu quin prius fuerit in sensn. 

That is why St. Thomas held that in the first operation of the 
intellect, the one that we have described above as ' simple appre- 
hension,' there is, on the part of the human mind, not even a 
possibility of error — and that error can occur only in the second 
operation (judgment) or in the third (reasoning). With the ex- 
amination of these last propositions we shall conclude the present 
study. 

First of all, no error can occur in the process of the first opera- 
tion of the mind, the ' simple apprehension,' except inasmuch as 
judgment mixes with it to some extent. 2 That assertion is already 
manifest from the analysis of the process of abstraction that we 
have given above. In the presence 6f the object, the intellect may 

1 loc. cit. 

2 Ibid., q. 85, a. 5. 



626 THE PHILOSOPHICAL REVIEW. [Vol. XII. 

or may not advert to it. If it does not, no intellectual action will 
take place, and therefore there will be no error because no act 
of intelligence ; if, on the contrary, the intellect does advert to the 
object as presented by the imagination, and an act of intelligence 
does indeed take place, it will understand the object fully or at 
least partially. If some person comes toward me in the dark, I 
may recognize that this is a human being, without, however, being 
able to discern what person it is. In that case, I shall gather 
only partial information, but a partial truth implies no error of 
itself except in so far as my mind may mistake that partial truth 
for a complete one. 

If in the presence of some dubious animal, let us say a coral, 
for instance, I notice in it some vegetative properties, without, 
however, discovering the animal characteristics that are to be 
found in it at the same time, and if, therefore, I gather from that 
incomplete observation the idea that there is something vegeta- 
tive in the coral, there is as yet no error in that partial truth, un- 
less I judge that a coral is only and exclusively a plant ; but 
forming such an erroneous opinion is going beyond the limits of 
simple apprehension, is launching into a judgment, into the sec- 
ond operation of the mind, in which, as well as in the third, viz., 
reasoning, no natural privilege of immunity from error can be 
guaranteed to us. 

The causes of the errors that may befall the individual mind in 
its search for truth are subtle and manifold ; all of us are more 
or less doomed to fall into mistakes now and then, but this is no 
proof that the human mind itself is not made for truth, or is in- 
capable of reaching it. There is no reason why we should at all 
doubt of its inherent capacity to grasp truth. Judgment, there- 
fore, and reasoning are also operations by which we are capable of 
attaining to the truth. This will be our concluding proposition. 

Judging is mentally associating or dissociating two concepts, 
two essences, on the basis of some characteristics that they have 
in common. 1 Having, for instance, perceived the idea of animal 
and that of biped, I may form the judgment : 'An animal may 
be a biped.' Now the two ideas that are thus associated in the 

1 Sum. theol., Part I, q. 85, a. 5. 



No. 6.] AQUINAS' S PHILOSOPHY OF KNOWLEDGE. 627 

foregoing judgment are, as we have shown, objective in their origin 
and objective in their representative value. Supposing, therefore, 
that a judgment is not founded on ignorance, or an imperfect 
knowledge of the two elements involved as subject and predicate, 
the mutual agreement on which my judgment is based is inherent 
in those two ideas themselves ; but then it must exist also in the 
things that are represented by those ideas, and of which they are 
merely the mental substitutes, the intellectual likenesses. We 
have, therefore, consistently to admit that our judgments have a 
real objective value in and through the ideas on which they are 
based. 

Reasoning, as St. Thomas remarks, 1 is a property of the hu- 
man intellect founded on its relative weakness and inferiority, 
that makes it unable to embrace the whole domain of truth at 
one glance, and to discover at once all that is contained in one 
idea. This makes it necessary for it to grope its way, to run suc- 
cessively {discurrere) from one judgment to another, so as to pro- 
ceed from known propositions to unknown truths. It may, 
therefore, be defined as the process by which, be it inductive or 
deductive, on the basis of two given mental judgments, we are 
enabled by bringing them together to perceive the truth of a third, 
which, without the help thus afforded by the two first, would either 
never have occurred to us, or would have remained forever dubious 
in our minds, exactly as the meeting of two electric currents, the 
positive and the negative, will cause an electric spark to flash in 
the darkness. 

Here, again, while having more than sufficient motives for dis- 
trusting the capability of the individual mind, there is no cause 
why we should doubt the objective value of the reasoning proc- 
ess in itself, provided all the necessary precautions against a 
possible error be taken. For if the two premises are objectively 
true and fully understood, and if no flaw finds its way into the 
process of comparison, the third judgment that springs from it 
must also be considered as objectively true and reliable, since it 
is but the inherent and natural content of objectively valid judg- 
ments. We are therefore entitled legitimately to extend the con- 
clusion of our reasonings to the objective world without. 

1 Qu&st. disput. de verit., q. 15, a. I. 



628 THE PHILOSOPHICAL REVIEW. 

To sum up in one sentence the whole epistemological system 
of Aquinas, we should say : Man's mind is, in itself, a faithful 
mirror of the external universe, that mirrors itself in it ideally 
and immaterially. Such would be, on the principles of St. 
Thomas, the outcome of the foregoing study. 

Readers who have had the patience to read the present article 
thus far, will find perhaps that we have touched upon a great 
number of questions, while leaving an even greater number un- 
touched. Our excuse is that this exposition could not be more 
than an epitome of the principal tenets of the Thomistic system, 
and that, if thoroughly developed and enlarged to its proper 
size, it might easily fill several volumes. If, however, we have 
succeeded in making it sufficiently suggestive to induce some re- 
flective minds to turn to St. Thomas himself, we shall be fully 
satisfied with the result. Nothing can supply the want of direct 
contact with the text and the knowledge of an author which 
we obtain by communing immediately with his thoughts in his 
own original works. Thus only from a conscientious and 
careful study, can one expect to experience that ' rest of mind ' 
(<juies animi) in the possessed truth, in which Aquinas, in con- 
formity with the dicta of the great Aristotle, made the natural 
beatitude of the soul consist — that rest being the loftiest enjoy- 
ment of our noblest faculty exercised about its highest possible 
object. 

F. L. van Becelaere. 
Ottawa.